virt July 2009

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39 participants
66 discussions

[PATCH] Change libguestfs to use virtio block devices
by Richard W.M. Jones 01 Jul '09

01 Jul '09

The following set of patches changes libguestfs to use virtio block devices by default. Device names change from /dev/sd* to /dev/vd*, but device name translation should hide this change in most cases: http://libguestfs.org/guestfs.3.html#block_device_naming The change isn't totally straightforward. The CHS for virtio disks is different from the CHS for IDE disks (even where the disks have identical size). These caused sfdisk with explicit cylinder numbers to fail, so I had to change all these. This is the reasoning behind patch 2 and most of patch 3. Patch 1: Just changes the way some messages are displayed from the test suite. Patch 2: Changes the statvfs test so it doesn't get affected by the CHS change. Patch 3: (a) We change the list-devices and list-partitions functions so that they see and return /dev/vd* devices. (b) The udev fix previously posted to this list. (c) Change the partition sizes because of the CHS change - see above. (d) Add ,if=virtio to -drive parameters so that block devices are exported as virtio disks. Patch 4: The generated code, just shown for completeness. The tests all pass except one. A single test fails because pvremove from the previous test causes sfdisk to fail (apparently the previous pvremove is still happening, so sfdisk refuses to partition the device because it is in use). I believe this is an underlying failure revealed by this change to virtio, not caused by the change itself. There doesn't appear to be any noticable increase in speed when running the tests, but I didn't measure anything. The main reason to use virtio is that it's inherently simpler than emulating IDE or SCSI devices. Rich. -- Richard Jones, Emerging Technologies, Red Hat http://et.redhat.com/~rjones libguestfs lets you edit virtual machines. Supports shell scripting, bindings from many languages. http://et.redhat.com/~rjones/libguestfs/ See what it can do: http://et.redhat.com/~rjones/libguestfs/recipes.html

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[PATCH] add comments suggesting memory-handling improvements
by Jim Meyering 01 Jul '09

01 Jul '09

Hi Rich, Looking at the sole remaining uses of asprintf, I noticed these and some realloc/strdup results that needed to be checked. Re asprintf, note that one must always check it for failure, and when it fails, you cannot use the (undefined) pointer result. Obviously this patch is just for reference, i.e, not to apply. >From 7b7df29516dad78a3c815ea1ef301da89d4b5323 Mon Sep 17 00:00:00 2001 From: Jim Meyering <meyering(a)redhat.com> Date: Wed, 1 Jul 2009 16:09:33 +0200 Subject: [PATCH] add comments suggesting memory-handling improvements * fish/destpaths.c: Don't deref NULL or undef on failed heap alloc. --- fish/destpaths.c | 13 ++++++++++--- 1 files changed, 10 insertions(+), 3 deletions(-) diff --git a/fish/destpaths.c b/fish/destpaths.c index 6cddafa..a5ece2a 100644 --- a/fish/destpaths.c +++ b/fish/destpaths.c @@ -55,7 +55,7 @@ complete_dest_paths_generator (const char *text, int state) static int len, index; static char **words = NULL; - static int nr_words = 0; + static int nr_words = 0; // nr_words should be size_t char *word; guestfs_error_handler_cb old_error_cb; void *old_error_cb_data; @@ -75,6 +75,7 @@ complete_dest_paths_generator (const char *text, int state) char **strs; int i, n; + // len should be of type size_t; index and "i", too len = strlen (text); index = 0; @@ -92,8 +93,11 @@ complete_dest_paths_generator (const char *text, int state) #define APPEND_STRS_AND_FREE \ if (strs) { \ + // n should be unsigned, like size_t n = count_strings (strs); \ + // handle the case in which sizeof (char *) * (nr_words + n)) overflows words = realloc (words, sizeof (char *) * (nr_words + n)); \ + // handle failed realloc for (i = 0; i < n; ++i) \ words[nr_words++] = strs[i]; \ free (strs); \ @@ -120,17 +124,20 @@ complete_dest_paths_generator (const char *text, int state) p = strrchr (text, '/'); dir = p && p > text ? strndup (text, p - text) : strdup ("/"); + // handle failed strdup strs = guestfs_ls (g, dir); /* Prepend directory to names. */ if (strs) { for (i = 0; strs[i]; ++i) { + int err; p = NULL; if (strcmp (dir, "/") == 0) - asprintf (&p, "/%s", strs[i]); + err = asprintf (&p, "/%s", strs[i]); else - asprintf (&p, "%s/%s", dir, strs[i]); + err = asprintf (&p, "%s/%s", dir, strs[i]); + // handle failed asprintf, i.e., err < 0 free (strs[i]); strs[i] = p; } -- 1.6.3.3.483.g4f5e

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libguestfs and yum
by David Huff 01 Jul '09

01 Jul '09

Anyone see any issues with libguestfs and yum working weirdly?? If I mount an disk image with guestfish and try to install new packages with yum, it gives rpmdb errors. However if I "launch" the disk images as a guest in a fill virt container like qemu, there are no rpmdb error and I can install new packages with yum.... Also, if I remove the rpmdb and rebuild via guestfish, then yum seems to be working fine.... command "rm -f /var/lib/rpm/__db.004" command "rpm --rebuilddb" Then yum seems to work: command "yum install vim-enhanced" It looks like yum is still using something outside of guestfish, anyone have any comments/ideas on this?? Thanks, David

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best Fedora virtualization
by Rich Mahn 01 Jul '09

01 Jul '09

I am planning on running several virtual machines on a single host. I will have two or three Linux baeed virtual machines and one or two Windoze. I plan on using a F11 host system. I need most of these to run automatically on boot-up of the host system. It would be really nice if I could use something like the Ctl-Alt-FN to be able to access and switch between virtual machines. This needs to be stable. The machines that these virtual machines are intended to replace are often running hundreds of days between reboots. My gut feel is that the virt-manager suite might be the way to go, editting the apropriate xml files as required. I also see there is a qemu launcher and it seems to work okay. I suspect there are others as well. What tends to be the consensus here on the various virtual machine managers? Are there white papers somewhere that could give some insight? Thanks Rich

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disk perf again
by Tom Horsley 01 Jul '09

01 Jul '09

In my xen virtual machines, I found that switching my disk image files from file: to tap:aio: made the machines (all HVMs) run much better with far fewer hangs and glitches. If I were to try to run with KVM rather than XEN, is there some equivalent of something like tap:aio that provides better disk performance, or is the KVM equivalent of file: the only way to access a disk image in a file? (I hasten to add I have absolutely no idea what the heck file: versus tap:aio: means, I just tried it when I saw it mentioned somewhere and it worked much much better :-).

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[PATCH] don't dereference or free undefined "msg" upon OOM
by Jim Meyering 01 Jul '09

01 Jul '09

Hi Rich, Here's a tiny patch to prevent misbehavior on an OOM failure: I prefer the decl-after-stmt (c99) syntax, but if you're not assuming that already, just move the declaration of err "up". >From bb57a823975019ab1be6f5f88e8276b53e8b4023 Mon Sep 17 00:00:00 2001 From: Jim Meyering <meyering(a)redhat.com> Date: Wed, 1 Jul 2009 15:45:01 +0200 Subject: [PATCH] don't dereference or free undefined "msg" upon OOM * src/guestfs.c (guestfs_error): Handle failing vasprintf. --- src/guestfs.c | 4 +++- 1 files changed, 3 insertions(+), 1 deletions(-) diff --git a/src/guestfs.c b/src/guestfs.c index 5743a07..87b0d86 100644 --- a/src/guestfs.c +++ b/src/guestfs.c @@ -404,9 +404,11 @@ guestfs_error (guestfs_h *g, const char *fs, ...) char *msg; va_start (args, fs); - vasprintf (&msg, fs, args); + int err = vasprintf (&msg, fs, args); va_end (args); + if (err < 0) return; + if (g->error_cb) g->error_cb (g, g->error_cb_data, msg); set_last_error (g, msg); -- 1.6.3.3.483.g4f5e

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virt July 2009